The invention relates to a thermostatic safety valve for a hydraulic cooling circuit, in particular for an internal combustion engine.
Such a valve is known and serves to interrupt the flow of cooling liquid to the radiator until the temperature of the engine has reached a determined value. The valve comprises a cage inserted in the cooling liquid circuit and defining an upstream chamber and a downstream chamber with communication between the chambers being controlled by a moving valve member suitable for co-operating with a fixed seat and carried by a thermostatic capsule subjected to opposing forces from a spring and from a thermally expandable material that it contains.
In a first embodiment that is presently in use, the thermally expandable material is a wax whose melting temperature corresponds to the action temperature selected for the valve. The thermostatic capsule seals one of the ends of a deformable sheath covering a rod fixed in the capsule downstream from the seat, and the wax fills a cavity of the capsule extending around the sheath. The valve member is carried by the capsule and the sheath is pressed against the cage.
So long as the valve member is pressed against its seat and interrupts any communication between upstream and downstream, the capsule is immersed in the upstream chamber and heats up on contact with the cooling liquid coming from the engine. The wax changes state and increases in volume on going from the solid state to the liquid state. Under such conditions, the capsule moves away from the rod in an upstream direction and increases the volume of the wax-containing cavity; as a result the valve member is lifted off its seat by moving in an upstream direction.
In the event of wax leaking out or of the cage breaking, the spring holds the valve member closed and temperature rises. Cooling is no longer performed and the engine becomes abnormally hot: it must be stopped to avoid worse damage such as rupture of the cylinder head gasket, seizing and damage to the engine itself, . . . .
In a second prior embodiment, the thermostatic capsule is a tubular bellows that is fluted to deform axially and that contains a liquid such as alcohol, ether, or some other liquid whose saturated vapor pressure corresponds to the intervention temperature selected for the valve. When the cooling liquid from the engine reaches said temperature while the valve is closed, then the capsule subjected to the saturated vapor pressure lengthens and opens the valve member in the downstream direction. If substance should leak out or the cage should break, then the valve member remains pressed against its seat and the same drawbacks as above appear.
In a third embodiment, the thermostatic capsule is similar to that of the first embodiment, and bears at its upstream end against the cage and the rod carrying the valve member. In the event of substance leaking out or of the cage breaking, the valve member likewise remains stuck against its seat.